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The Comparative Effects of Cottonseed Oil and Lard on Cholesterol Levels in the Tissues of Rats^{1, 2, 3,}

Department of Biochemistry and Nutrition, School of Medicine, University of Southern California, Los Angeles

Plasma and liver cholesterol levels and liver lipids of male and female rats maintained on diets containing 15% lard or 15% cottonseed oil, with and without cholesterol, were determined after 6, 12, 18 and 24 weeks. In all cases, higher cholesterol concentrations were found in the livers of animals on the lard diets. Differences in plasma cholesterol levels and total liver lipids were not apparent unless cholesterol was present in the diet, at which time animals receiving the cholesterol-supplemented lard diets exhibited higher cholesterol concentrations in these categories as well.

A sex difference in cholesterol metabolism has been observed; on both dietary regimens, female rats exhibited higher plasma and lower liver cholesterol levels than those found in the corresponding male rats.

Increased cholesterol concentrations were also noted in the carcasses (excluding liver) of animals of both sexes which had been fed the diet containing lard as compared with the cholesterol content of carcasses of animals on the cottonseed oil diet.

The absorption of cholesterol in male and female rats when fed with either lard or cottonseed oil was found to be the same regardless of the vehicle. However, a sex difference in lipid metabolism was again exhibited, since on both lipid diets, female rats absorbed more cholesterol than did the male rats.

The possibility that the small quantities of cholesterol present in lard might account for the increased liver cholesterol in the animals on this diet was eliminated, since, when the cholesterol content of cottonseed oil was equalized with that normally present in lard, no effect on liver and plasma cholesterol levels as compared with regular cottonseed oil was observed.

The effect of vitamin E, in which lard is practically deficient, was studied by adding a 5-fold excess of vitamin E to the lard diets with and without cholesterol. The increased quantities of vitamin E definitely decreased the liver cholesterol concentration of the rats fed cholesterol to a point where the differences in liver cholesterol content of animals on both the lard + cholesterol diet and the cottonseed oil + cholesterol diet were non-existent. Vitamin E, however, was without effect in the rats on the lard diet from which exogenous cholesterol was omitted.

It is hypothesized that the difference in action of the two fats is due to the greater quantity of essential fatty acids found in cottonseed oil over that which occurs in lard. These essential fatty acids are required for normal cholesterol transport and metabolism; and inadequate supply will tend to cause the accumulation of cholesterol in certain tissues in the animal body.

² Presented in part at the meetings of the Federation of Societies for Experimental Biology, Atlantic City, 1956.

³ Contribution no. 418 of the Department of Biochemistry and Nutrition, University of Southern California, Los Angeles.

⁴ Deceased, April 17, 1956.

Manuscript received 17 November 1956.